It's a bit of a pain in the ass, but if you don't mind the extra time and work you can drill/ream the berdan anvil and convert it for use with boxers.
I was looking for this same thing a while back and found someone else had done this with good success and documented the process. http://users.ameritech.net/mchandler/primer.html" onclick="window.open(this.href);return false;
....if you are really bored some evening and happen to have some spent steel cases that are berdan primed and your curiosity overcomes your better sense, it can actually be done, but it is (hypothetically speaking ) a fair bit more anoying than brass.
Good luck

True. There are at least 6 different Berdan sizes that I'm aware of (and likely more). For some of the slightly smaller pockets, you can ream them out to .209 for a tight fit (assuming the case head has enough material to support the change). For some of the larger Berdans I've seen guys make a collet out of a .22 casing and that apparently works ok if there arn't any other options....if I had a gun and calliber that I really liked that much I would probably just find a similar boxer primed cartridge and then find some dies to reform it.